A seat slide apparatus for a vehicle including an upper rail retaining a seat above the upper rail and a lower rail retaining the upper rail in a state where the upper rail moves relative to the lower rail is known. In addition, for example, JP2008-44518A, hereinafter referred to as Reference 1, discloses a seat slide apparatus having a configuration where a rolling element is arranged between a lower rail and an upper rail. In the seat slide apparatus according to Reference 1, a retaining member retains the rolling element between the lower rail and the upper rail. The retaining member includes a protruding portion that is configured to slidably contact with a rolling surface in a state where the protruding portion makes pressure contact with the rolling surface. Note that the rolling surface refers to a surface on either the lower rail or the upper rail at which the rolling element retained by the retaining member rolls.
More specifically, rolling of the rolling element, which is in contact with each of the lower rail and the upper rail, may provide a smooth movement of the lower rail and the upper rail relative to each other in a state where the lower rails and the upper rails move relative to each other in accordance with a seat slide operation. The protruding portion is arranged on the retaining member to provide a comfortable operational feeling and a distinct control feeling to the seat slide operation by a frictional force at the protruding portion, which is appropriately restraining the excessively smooth movement.
Nevertheless, in a configuration where a rolling element is arranged between a lower rail and an upper rail, smooth rolling of the rolling element thereat is of at most importance. For example, in a seat slide apparatus for a vehicle, a foreign object may enter between a lower rail and an upper rail of the seat slide apparatus. Quality of operational feeling may lower due to a presence of the foreign object that interferes with smooth rolling of the rolling element, which is considered as a drawback.
A need thus exists for a seat slide apparatus for a vehicle, which is not susceptible to the drawback mentioned above.